Zmodo Greet

"Although the information we release has been verified and shown to work to the best our knowledge, we cant be held accountable for bricked devices or roots gone wrong."
This page will be dedicated to a general overview of descriptions and information related to The Zmodo Greet

Contents

Purchase

About

The Zmodo Greet is a WiFi doorbell with a camera and two way audio communication.

Power

Powering this board is a bit of a challenge. It expects to be connected to a 10-36V AC source in series with a doorbell chime. Just connecting a DC source to the input doesn't work. We found the best method is to solder a connection to the DC side of the rectifier and supply a low DC voltage there (we used a 9V battery).

UART

The main board has a UART broken out to two test points on the back. During boot you can use this UART to get a U-Boot shell. Once the device has finished booting the UART presents a root busybox shell. The UART runs at 115200 baud.

Demo

Software Vulnerabilities

While the Zmodo Greet is in setup mode it hosts a WiFi network and accepts an HTTP request to configure the device. This HTTP request is handled by a CGI binary that has a serious buffer overflow vulnerability.

If you connect to the setup network, you can use this curl command to cause the binary to crash:

This causes the process to jump to the address 0x61616160 ("AAA`" in ASCII). With some development this could be made into a remote code execution attack. The device does have ASLR enabled, so it will take some work to make a viable payload.